Mechanical, Electronic, and Thermodynamic Properties of Zirconium Carbide from First-principles Calculations*Project Supported by the National Natural Science Foundation of China (Grant No. 51071032). PDF Download
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Languages : en
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Abstract: Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic constants are all well consistent with the experimental data. The electronic band structure indicates that the mixture of C 2p and Zr 4d and 4p orbitals around the Fermi level makes a large covalent contribution to the chemical bonds between the C and Zr atoms. The Bader charge analysis suggests that there are about 1.71 electrons transferred from each Zr atom to its nearest C atom. Therefore, the Zr–C bond displays a mixed ionic/covalent character. The calculated phonon dispersions of ZrC are stable, coinciding with the experimental measurement. A drastic expansion in the volume of ZrC is seen with increasing temperature, while the bulk modulus decreases linearly. Based on the calculated phonon dispersion curves and within the quasi-harmonic approximation, the temperature dependence of the heat capacities is obtained, which gives a good description compared with the available experimental data.
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Languages : en
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Abstract: Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic constants are all well consistent with the experimental data. The electronic band structure indicates that the mixture of C 2p and Zr 4d and 4p orbitals around the Fermi level makes a large covalent contribution to the chemical bonds between the C and Zr atoms. The Bader charge analysis suggests that there are about 1.71 electrons transferred from each Zr atom to its nearest C atom. Therefore, the Zr–C bond displays a mixed ionic/covalent character. The calculated phonon dispersions of ZrC are stable, coinciding with the experimental measurement. A drastic expansion in the volume of ZrC is seen with increasing temperature, while the bulk modulus decreases linearly. Based on the calculated phonon dispersion curves and within the quasi-harmonic approximation, the temperature dependence of the heat capacities is obtained, which gives a good description compared with the available experimental data.
Author: B. D. Pollock
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Category : Thermodynamics
Languages : en
Pages : 24
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Author: Yue Zhou
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Languages : en
Pages : 129
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"This research focused on the synthesis and phase formation of zirconium carbide with different carbon contents, and lattice thermal conductivity of zirconium carbide with different carbon vacancy, hafnium, and oxygen contents. Nominally pure phase ZrC[sub x] was synthesized by solid-state reaction of zirconium hydride (ZrH2) and carbon black at a temperature as low as 1300°C. The powder synthesized at 1300°C was carbon deficient ZrC[sub x]. Carbon stoichiometry of the as-synthesized powders increased as the synthesis temperature increased. As the synthesis temperature increase, the oxygen content of ZrC[sub x] decreased due to the increasing C site occupancy. Low stoichiometry ZrC[sub 0.6] powders were synthesized at 1300°C and 2000°C, and the formed phases were investigated. Carbon vacancy ordered phases were detected by neutron diffraction and selected area electron diffraction. Lattice thermal conductivities of ZrC[sub x] with different carbon contents (x=1.0, 0.75, 0.5) and different hafnium contents (3.125 at% and 6.25 at% were studied theoretically. A combination of first-principles calculations and the Debye-Callaway model was employed to predict the lattice thermal conductivities. Lattice thermal conductivities of all the compositions decreased as temperature increased. Increasing carbon vacancy content reduced the lattice thermal conductivity while increasing the grain size increased the lattice thermal conductivity. Lattice thermal conductivities of ZrC[sub x] also decreased as the content of Hf increased. Carbon vacancies and Hf impurities decreased the phonon transport, thus the lattice thermal conductivity decreased"--Abstract, page iv.
Author: Nicole Mary Korklan
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Category :
Languages : en
Pages : 51
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Author: M. H. Leipold
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Category : Zirconium carbide
Languages : en
Pages : 14
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Languages : en
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